docs: def upsert(self, dataset_identifier, payload, content_type="json"):
          '''
          Insert, update or delete data to/from an existing dataset. Currently
          supports json and csv file objects. See here for the upsert
          documentation:
              http://dev.socrata.com/publishers/upsert.html
          '''
          resource = _format_new_api_request(dataid=dataset_identifier, content_type=content_type)
  
          return self._perform_update("post", resource, payload)